PROJECT SUMMARY Amyotrophic Lateral Sclerosis (ALS) is a 100% fatal neuromuscular disease with the majority of patients dying 2-5 years after diagnosis. ALS results in progressive weakness and eventual paralysis of voluntary skeletal muscles in the arms, legs, head, neck, and those involved with respiration. In particular, weakness of the head and neck muscles (bulbar muscles) result in speech & swallowing impairment, also known as dysarthria and dysphagia, respectively. Both conditions are associated with major depression in ALS; however, dysphagia is highly correlated with malnutrition and aspiration pneumonia, which significantly contribute to morbidity and mortality in ALS patients. The underlying cause of ALS is largely unknown; however, decreased levels of the neurotransmitter serotonin (5-HT) in the central nervous system (CNS) and circulatory system have been reported in human ALS patients and mouse models of the disease. Furthermore, patients will bulbar symptoms have an even greater impairment of their serotonergic systems. Though 5-HT abnormalities have been noted in the CNS, approximately 95% of the body?s 5-HT is produced in the gastrointestinal (GI) tract which supplies the body with 5-HT via blood platelets. It has been shown that a mouse model of ALS has morphological and molecular changes in its GI tract that result in alterations of the intestinal microbiota, which in turn may alter the body?s serotonin production. We hypothesize that serotonin supplementation in a mouse model of ALS will restore 5-HT levels in the CNS, blood, and GI tract, thus extending the life span and delaying communication & swallowing deficits. The long- term goal of this proposed research is to explore the role of 5-HT in the pathophysiology of ALS, specifically regarding bulbar impairment, while investigating potential therapeutics. The overall objective is to establish an effective treatment protocol for improving speech & swallow function utilizing serotonin supplementation. For this proposal, we will study a transgenic mouse model of ALS (SOD1-G93A, low copy expressing) and age- matched littermate controls. Mice will receive serotonin supplementation 3X/week from disease onset (6 months) to end-stage (~9 months) for comparison with untreated controls. We will utilize ultrasonic vocalization and videofluoroscopic swallow study assays monthly to assess speech and swallow function, respectively, over time. Serotonergic activity in the CNS, blood, and GI tract will be examined using high performance liquid chromatography, immunohistochemistry, and quantitative polymerase chain reaction. For these serotonin assays, tissues and blood will be collected at 3 different study endpoints: pre-symptomatic (4 months), disease onset, and disease end-stage. Results will provide in-depth knowledge of the serotonergic system that is largely unexplored in ALS, specifically in regard to the GI tract. This study will provide the groundwork for additional mechanistic studies involving serotonin in pre-clinical animal trials and clinical human investigations.